1. Field of the Invention
The present invention generally relates to a circuit board and a manufacturing method thereof, and more particularly, to a circuit board and a manufacturing method thereof with effective laser machining depth control.
2. Description of Related Art
Today's market demands electronic products to be designed small, slim, light, and highly portable. Accordingly, electronic parts in these electronic products have to be designed small and thin too. Thereby, a conventional technique for reducing the thickness of a portion of a circuit board is provided.
FIGS. 1A-1C are cross-sectional views illustrating a conventional circuit board manufacturing process, and FIG. 2 is a top view of a circuit substrate in FIGS. 1A-1C, wherein FIGS. 1A-1C are cross-sectional views illustrating the conventional circuit board manufacturing process along line I-I′ in FIG. 2.
First, referring to both FIG. 1A and FIG. 2, a circuit substrate 100 having a first dielectric layer 110, a second dielectric layer 120, a circuit layer 130, a third dielectric layer 140, and a fourth dielectric layer 150 is provided. The second dielectric layer 120, the third dielectric layer 140, and the fourth dielectric layer 150 are sequentially stacked on the first dielectric layer 110, and the circuit layer 130 is disposed on the second dielectric layer 120 and located between the second dielectric layer 120 and the third dielectric layer 140. The circuit substrate 100 has a pre-removing area L.
Then, referring to FIG. 1B, the portions of the third dielectric layer 140 and the fourth dielectric layer 150 located at the periphery of the pre-removing area L are removed through laser machining. Next, referring to FIG. 1C, the portions of the third dielectric layer 140 and the fourth dielectric layer 150 located within the pre-removing area L are removed to form a removing area L1. Herein a circuit board P is roughly formed. Because the removing area L1 of the circuit board P is thinner than other areas of the circuit board P, an electronic device 200 may be disposed within the removing area L1 in an actual application to reduce the total thickness of the circuit board P and the electronic device 200 disposed thereon.
However, it is difficult to control the depth of the laser machining when the third dielectric layer 140 and the fourth dielectric layer 150 are removed through laser machining. As a result, the second dielectric layer 120 or even the first dielectric layer 110 may be over trenched.